It is estimated that an average of 700 water mains will break in cities and towns across North America in an average day. In the course of one year, 250,000 main breaks will cost North America more than $1 billion.
Most people believe that old age is the primary contributor to iron water main breaks. However, the problem isn?t age. It is corrosion. An older pipe can continue to operate as long as corrosion is controlled.
The majority of water piping installed in the 20th century was cast or ductile iron, which was expected to provide water utilities with 50 to 100 years of trouble-free service. Unfortunately, these pipes are susceptible to corrosion and subsequent breakage.
Many factors contribute to corrosion-induced water main breaks, including soil conditions, coupling to dissimilar metals, seasonal temperature changes, soil stress, road de-icing salts, seismic action and stray electrical currents.
Older cast iron pipe consists of flakes of graphite (carbon) in an iron matrix. When the metal corrodes, it loses the iron constituent, leaving behind the graphite. Pipe that has turned to graphite often retains the appearance of sound pipe, leading casual observers to mistakenly believe the pipe has remained corrosion-free for many years. However, the pipe fractures easily because it lacks the strength and ductility of the original iron. Any increase in the external or internal stress on brittle, corroded pipe can quickly result in a break.
Ductile iron pipe, introduced to water systems in the 1950s and still in use today, was intended to offer better quality than cast iron. However, the pipe?s matrix and thinner wall make it vulnerable to pitting corrosion attack.
The technology of cathodic protection has been successfully applied to a wide variety of buried metallic structures for years. In fact, government agencies have mandated cathodic protection on buried gas and oil pipelines since the 1970s, and on steel underground storage tanks since the 1980s.
To protect pipes, galvanic anodes are strategically placed on existing cast and ductile iron water mains. The higher energy level of the anode allows current to discharge to the pipe, causing the anode to corrode instead of the pipe. This process reduces breaks, saves the cost of needless repairs and extends service life.
Corrpro?s Break Reduction/Life Extension program collects field data, examines leak histories and uses computerized technology to identify weaknesses or hot spots. The company provides pipeline evaluation, maintenance and consulting as well as installation and maintenance of cathodic protection system. The company can retrofit existing water lines with galvanic anode cathodic protection systems designed to extend the life of these pipe systems and minimize failures.
About the Author:
Jim Lary is a NACE certified corrosion engineer and Vice President at Corrpro Companies, Inc. The company specializes in corrosion control and non-destructive testing.